The proposed research concerns a DNA helix destabilizing protein (HDP) purified from rat liver by the principal investigator. Following aspects of HDP will be investigated in vivo during the course of cell cycle in synchronized cultures, and at different times during dexamethasone induced transcripton in hepatoma tissue culture (HTC) cells; anti-HDP rabbit sera, already generated, will provide the desired specificity and sensitivity: (a) cellular localization by immunocytochemical techniques; (b) quantitation in cytoplasmic and nuclear extracts by radioimmunoassay; (c) rates of synthesis and post-synthetic modifications by pulse labelling with isotopic amino acids and appropriate substrates for side chain modifications; (d) cytonuclear transport by quantitating the labelled protein in cytoplasm and nucleus during a "cold" chase; and (e) turnover of the protein and its side-chain moiety. Temporal correlation of data from these experiments in vivo with levels of replication and transcription in chromatin will indicate whether HDP is involved in synthesis of DNA or RNA, or both. Also, metabolism of side-chain moieties may provide a glimpse at putative mechanisms for regulation of HDP. Supportive evidence will be obtained from effects of HDP on DNA and RNA polymerase reactions in vitro. Analyses of chemically modified HDP and resultant effects on its helix destabilizing activity also will be carried out to explore the molecular basis of its activity.